MOUNT WILSON OBSERVATORY. 



245 



Preliminary Test of the Thalofide Cell. 



Observations of stars with a thalofide cell, supplied by the Case 

 Research Laboratory, have been made with the 60-inch and 100-inch 

 telescopes by Messrs. Benioff and Shapley. Several different arrange- 

 ments of the apparatus have been tried, using either an electrometer or 

 a galvanometer, the latter with and without an audion amplifier, and 

 large deflections have been obtained in some cases. It seems probable 

 that a special form of cell, with suitable auxiliary apparatus, will prove 

 effective in practice. 



STELLAR SPECTROSCOPY. 



The systematic stellar spectroscopic work during the year has been 

 carried on by Mr. Adams, Mr. Joy, Mr. Merrill, Mr. Sanford, and Mr. 

 Stromberg. Mr. Duncan and Mr. Hoge have also conducted observa- 

 tions during a portion of the year. Both of the large reflectors have 

 been in regular use and the spectroscopic equipment with the two 

 instruments has been similar in character, a spectrograph with a dis- 

 persion of one dense flint prism and a camera of 45 cm. focal length 

 being used at the Cassegrain focus for a large proportion of the photo- 

 graphs. The 18-cm. camera has been employed in the case of a few 

 very faint stars. 



Of 1,484 spectrograms obtained during the year, 591 have been made 

 with the 100-inch reflector and 893 with the 60-inch. Numerous 

 photographs of stars brighter than the sixth magnitude have been taken 

 with the 60-inch telescope, while the observations with the 100-inch 

 have been limited almost entirely to stars fainter than the eighth magni- 

 tude. The following sunmiary shows the number of spectrograms of 

 stars of different magnitudes taken with the two instruments: 



A large part of the work with the 60-inch telescope has been devoted 

 to stars under observation for absolute magnitude, while the objects 

 photographed with the 100-inch consist of faint stars of very large 

 proper motion, variable stars of type Md, certain faint Cepheid and 

 Algol variables, and a small number of Novse and miscellaneous objects. 



R.'U)iAL Velocitie.s. 



The principal results of the observations for radial velocity may be 

 summarized as follows: 



